1. Field of the Invention
The present invention relates generally to a telephone communication system and, in particular, to a device that provides a generic software interface to a digital line on one of many different types of digital phone switches. A telephone with such a generic interface is a "virtual phone" that has the flexibility to represent the majority of features of any digital phone, regardless of the switch type or the number of features in a digital phone.
The general concept of a virtual telephone has been in existence in various forms across different product lines. In some cases a virtual phone has been used to represent a specific digital phone, such as Rolm Phone 400 or a Meridian 2616. Those phones represent a superset of phones for their respective switches. In other cases a virtual phone has been used to represent only the necessary portions, or a subset, of a digital telephone.
2. Prior Art
One of the important characteristics of a telecommunication system is the ability of different interconnected components of the system to effectively communicate with each other. Many business-oriented telecommunication systems have PBX (Private Branch Exchange) switches that link internal telephones with each other and with external telephone networks.
Even though today most vendors build the PBXs around common available processors running common operating systems (such as UNIX) and use common programming languages (such as C or C++), unfortunately different vendors' switching devices use proprietary communication protocols. Thus, it is virtually impossible to integrate one vendor's switching device with other vendors' applications.
Therefore, it becomes highly desirable to provide a telecommunication system with a feature that would convert proprietary PBX or external application protocols into a common format, and thus would function as a "protocol interpreter" between proprietary switching system protocols and the protocols of various applications.
A number of solutions to that problem have been disclosed in the prior art. For example, U.S. Pat. No. 4,873,718 "Feature Telephone Integration Device" issued to Barnett et al discloses a device and method for integrating one vendor's application (a voice mail system) into a PBX environment of a different vendor. In that patent the interconnection was achieved by equipping the PBX vendor's feature phone with additional circuitry to monitor telephone communication between the PBX, the feature telephone and the external application. An obvious disadvantage of the disclosed system is its inability to provide a generic interface between many possible proprietary protocols of different PBX switching systems and an external application. The disclosed invention provided integration only between a PBX and a voice mail system, it did not provide for the possibility to integrate a PBX with a variety of different external applications. Moreover, any exchange of information about a call or a change of the status of the call occurs "one-way" only: from the PBX to the telephone set.
U.S. Pat. No. 5,440,616 provides an improvement over the device of U.S. Pat. No. 4,873,718 in the form of apparatus for interconnecting a messaging system (voice, facsimile, etc.) with a PBX which offers entirely digital transmission and provides high bandwidth and redundant transmission of control information between the messaging system and the PBX. The apparatus of U.S. Pat. No. 5,440,616 includes a digital voice terminal adapter which is a combination of hardware and software which emulates a digital feature phone and which interconnects a messaging system and a PBX to provide full integration of the messaging system with the PBX. The disclosed adapter does not, however, convert proprietary PBX or external application protocols into a common format and thus does not function as a protocol interpreter between proprietary switching system protocols and the protocols of various applications.
U.S. Pat. No. 5,255,314 "Switch Adjunct Integration Device" issued to Applegate et al discloses a device that uses multiple line appearances of one or more digital telephone lines to gather information on calls designed for an adjunct voice mail system. After receiving the required information the device transfers the calls to analog phone lines leading to the voice mail system. That device, again, provides no more than a communication tool between a PBX switch and a voice mail system. The disclosed device does not integrate any type of the known PBX switches with any type of external device via a generic interface.